1. Field of the Invention
The present invention relates to a device for processing optical signals without converting the optical signals into electrical signals, and in particular, it relates to the improvement of both the flexibility of an optical communications system and the system flexibility at each type of node point of an optical network.
2. Description of the Related Art
To enable high-speed large-capacity communications, at present an optical communications system is being developed and a part of the development is commercialized. Since such an optical communications system handles signals with a bit rate of 10 GHz and more, signals must be processed at speeds corresponding to these bit rates. However, if optical signals are converted into electrical signals, electronic devices cannot operate at a high speed such that optical signals can be handled, which is an obstacle to the implementation of the high-speed large-capacity optical communications described above. Therefore, to implement such high-speed large-capacity optical communications, fully optical devices for processing optical signals without converting the signals into electrical signals must be developed.
For a conventional method for branching/adding optical signals in order to implement the high-speed large-capacity optical communications, a method for processing wavelength-division-multiplexing (WDM) signals in a wavelength domain is generally used. When an optical signal control technology further progresses and each WDM signal channel is composed of high-speed large-capacity signals by optical time-division multiplexing (OTDM), the branching/addition of signals on a time axis will also be needed in the future.
However, the addition/branching of optical signals in OTDM described above requires a very high speed processing. Therefore, if optical signals are branched/added after being converted into electrical signals, the advantage of using optical signals in a sufficiently high-speed and large capacity communications cannot be utilized since the operation of electrical devices are slow.
Therefore, a configuration for enabling the branching/addition of high-speed OTDM signals without converting the signals into electrical signals is needed in the future.